Blood analysis is commonly carried out on a sample of whole blood which, for the majority of tests, is drawn from the vein of the arm, the finger or the earlobe. A number of tests and procedures have been developed and many can be carried out simultaneously on one blood sample with such instruments as automatic analyzers. While most hematological tests relate to the blood cells, in modem routine diagnostic testing, many tests are done on plasma or serum instead of the blood cells. Specifically, in recent years, an increasing number of immunochemical and nucleic acid analysis items have been developed. For instance, special tests can be used to detect substances contained in the plasma which are characteristic of specific infections such as HIV (Human Immunodeficiency Virus) particles.
In 2013, the World Health Organization (WHO) revised the current HIV treatment and prevention guidelines and emphasized the importance of HIV viral load (VL) testing in the management of HIV positive patients. Recently, WHO strongly recommends using HIV viral load testing to monitor the therapeutic efficacy of HIV Antiretroviral Therapy (ART) and also reduced the cutoff of the level of HIV plasma VL from 5000 copies/ml to 1000 copies/ml. In other words, if HIV patients under ART have a viral titer in plasma is greater than 1000 copies/ml, it will be considered as a drug treatment failure. Responses to treatment failure, such as adherence counseling, drug resistance testing and second line treatment regimens, are time-consuming and expensive, and should be used only if necessary. HIV viral load is normally measured using plasma as a specimen type. However, in resource limited settings, such as Africa, plasma samples may not be easily obtained, stored, transferred, and tested. Dried blood spots (DBS) have been evaluated as a solution for HIV viral load testing in the resource limited settings, with limited success. After infection, HIV virus not only starts to replicate itself in the infected cells, but also integrates its cDNA into the host chromosomes as the latent HIV proviral DNA (Greene, W. C. Peterlin, B. M. 2002. Nat Med. 8(7): 673-80). This additional cellular associated HIV Nucleic Acid can confound the determination of the VL of HIV when whole blood is used as the input sample material leading to unreliable determinations of treatment failure.
Accordingly, in view of performing such tests, there is an increasing need to separate plasma from the whole blood sample. Since these tests often involve sophisticated instruments, shipping of the plasma to specific analysis sites can be required. The European patent EP 1096254 B1 describes a device for separating hematocrit from a whole blood sample provided with an inlet port for receiving the sample, a reaction region and a capillary pathway connecting the inlet port with the reaction region. The capillary pathway which is provided with obstructions for keeping the blood cells back is integrally formed with the reaction region. U.S. Published Patent Application No. 2012/0088227 describes a device for separating plasma from a blood sample using a stacked structure having separating and absorptive members. The devices comprising a separation membrane and a plasma collection pad described by McClemon and McClemon (20th Annual DART Conference, Maui/Hawaii, USA, December 6-10, 2015) are easier to handle, however, there is still a risk of cross-contamination when removing the plasma collection pad. Further, it is required that the plasma collection or adsorbent pad can be easily removed from the device and, moreover, that the plasma sample is sufficiently stable for being further processed. In light of the foregoing, there is a need for an improved device and process for separating plasma from a whole blood sample.